In the course of training for a boxing match, and in the course of practicing to improve boxing skills, an important and major activity is actually sparring with another person, typically a boxer of comparable skill, or comparable weight and reach, sometimes a more skilled boxer or a trainer.
The most difficult part of sparring is to give the training or practicing boxer a realistic workout or at least an effective one that works towards improving skills, displaying them, or highlighting a technique that is in need of change or improvement, without unduly risking injury to the boxer or the sparring partner.
For a boxer, to spar has meant to rlsk injury at a moment when no title, prize or record is at stake, and, perhaps not only to become injured, but as a result to have to postpone or forego a match or other opportunity.
For a trainer, all too often the risk is so great that the trainer's observations and corrections to the boxer's technique must be offered from the perspective of a bystander, rather than from the perspective of a sparring partner. Particularly where the trainer's objectives are to keep a boxer's punches short and to prevent the boxer from punching to the outside, providing instruction as an observer or even as a participant in conventional sparring has been less than satisfactory.
A tendency in the past has been to attempt to replace a certain amount of sparring against a live partner, with practicing of punching against punching bags or other static or reactive mechanical targets. Although some of that type of practice no doubt is helpful, it gives the boxer a lesser sense of the vitality of an opponent. In short, the boxer misses out on refinement of his ability to effectively direct his punches at a mobile opponent when he is practicing against a static or merely reactive target.